1. The Field of the Invention
The invention relates to methods, systems, apparatuses, and kits for LC-MS separation and detection of analytes
2. The Relevant Technology
Liquid chromatography-mass spectrometry (LC-MS) is a powerful analyte detection and measurement technique that is quickly becoming the preferred method of detecting small molecule analytes for diagnostic purposes. However, the instrumentation required for LC-MS is technically complex and, as such, is typically not well suited to the average hospital clinical lab or medical lab technologist. By and large, these labs have not adopted LC-MS diagnostics and, instead, generally use alternative diagnostic techniques, including automated immunoassay, or send the samples out to a reference laboratory for analysis. Moreover, even reference laboratories or other types of testing laboratories including, without limitation, those for testing industrial or environmental samples would make broader use of LC-MS if the procedure was simplified and substantially automated.
Current LC-MS methods require careful selection of the appropriate liquid chromatography column and mobile phases for each different analyte of interest, as well as careful calibration of the mass spectrometer to isolate and identify the analyte of interest. In order to analyze a second different analyte on the same instrument, one or more of the column, the mobile phases, or the mass spectrometer settings generally must be changed and optimized by the LC-MS technologist. Because of the time and technical complexity of such changes, random access analysis of individual samples is costly and inefficient. So instead, samples flagged for analysis for the same or similar analytes are generally grouped into large batches and run together. While this arrangement may reduce the number of changes to the LC-MS system set-up from run-to-run, it significantly increases the time to result for each sample. The high complexity of the LC-MS setup and process calls for having an expert LC-MS technologist on hand all the time to make adjustments, manual changes, and hardware re-configurations to the system.
Since hospitals are typically not equipped or staffed to perform such sophisticated analytical chemistry experiments, LC-MS systems are generally not available at hospitals today. Instead, samples flagged for LC-MS analysis are sent out to a few central reference labs where samples are batched according to the ordered assay type(s). This practice is time-consuming and expensive. In addition, this situation makes it difficult for multiple analyses to be performed on the same sample. As a result, samples may be held for several hours or even days before their batch is analyzed and samples containing multiple analytes of interest may have to be aliquoted separately or placed back into the queue batch each time a different analyte is to be assayed. If the hospital is not near a major reference lab having LC-MS equipment, one must transport the sample to and from the lab, creating a further delay of possibly days. For time sensitive analyses (e.g., for emergency department patients or for samples containing unstable analytes), such delays are unacceptable. For more routine tests, such delays and added expense render many powerful LC-MS diagnostic tests simply unavailable today to many hospitals and diagnostic laboratories.
Efforts have been made to simplify LC-MS analysis by reducing the numbers of different columns and mobile phase buffers needed to purify and analyze a wide range of compounds having different characteristics. For example, Herman reported (Rapid Commun. Mass Spectrom. 16: 421-426, 2002) an LC-MS method to analyze a library of drug compounds for the purpose of drug-screening assays, not for diagnostic purposes, using one set of columns, one set of mobile phase buffers, and one set of liquid chromatography conditions (e.g., flow rate, isocratic elution, etc). The method of Herman is applicable to compounds having hydrophobicities spanning about 4 log partition coefficient (log P) units wherein detection within established clinical reference ranges and/or conformity to clinical standards are not required. However, the method of Herman is not applicable to extremely hydrophilic compounds (i.e., log P less than about 1) or to extremely hydrophobic compounds (i.e., log P greater than about 5).